mailed invoices coming back to my PO

Is there anyway that we can make our address and the clients address either both in bold or neither in bold? 20% + or – the Post office has mailed my invoices back to me, (double window envelopes) the gal at the Post office said there scannersmust be picking up the return address, because of the bold print. ❓ Any body else ❓
Thanks in advance